Minimally invasive tumor ablation is becoming an increasingly important tool to treat patients with cancer. The most popular modality, radiofrequency (RF) ablation, has been plagued by an unacceptably high post-treatment local recurrence rate. Microwave ablation has many of the same advantages as RF ablation, but in addition produces much higher heating, is very fast, and can support the use of multiple probes. If these advantages can be exploited, microwave should be a more effective cancer treatment than RF. However, systems in use in Asia use probes that are too large (14-gauge), and only create a small zone of necrosis (1.6 cm) which lead to the need for multiple overlapping ablations. This increases the invasiveness and complexity of the procedure, and leads to a higher complication and failure rate. The specific aims of this proposal are: 1) Develop a prototype triaxial microwave ablation device of 18 gauge or smaller that creates a zone of coagulative necrosis>2.0 cm in vivo. 2) Modify this device so that the resultant zone of ablation is scalable and controllable, and 3) Develop a convenient and low cost 2.45 GHz power source to be used for the experiments proposed in this application. We believe that our multidisciplinary team (Radiology, Computer and Electrical Engineering, Biomedical Engineering, Surgery, Pathology and Laboratory Medicine) can successfully complete this research program, and has a record of successful collaboration. If successful, this project should greatly increase the effectiveness of tumor ablation by decreasing treatment failures, costs, procedure length, and anesthetic complications. It is intended that this proposal will serve as a mechanism to gather preliminary data for a larger (R01) application.